Optical glass fibers have become integral to the telecommunications industry. While the fibers are exceptionally strong, they are easily flawed such as by exposure to environmental factors including dust and moisture. It is therefore desired to coat the fibers almost immediately after formation with one or more coating materials. In some cases these fibers have one coating material and in other cases two or more coatings may be used. For example, the fibers may be coated with a soft inner primary coating and a tougher secondary coating; the secondary coating typically provides a more durable exterior for the optical fiber. The outermost coating layer is often colored, such as by application of an ink layer or through addition of a colorant to the coating material itself. Color coding of the fibers allows for easier identification of the individual coated optical glass fibers. This is particularly relevant in industries where a plurality of fibers are aggregated into a cable. In such applications, the fibers are typically bonded together in a matrix material. For example, the matrix material can encase the optical fibers or can edge bond the optical fibers together.
It is generally desired that the matrix material used in optical fiber assemblies will provide both the desired level of “toughness” while still allowing for flexibility. The physical properties of the matrix components, such as the polymers, can be related to the performance of the matrix material. For example, a suitable matrix material will typically have a glass transition temperature (“Tg”) high enough to allow acceptable heat strip for peelable optical fiber ribbon and to provide resistance to environmental attacks such as by moisture and/or chemicals. The matrix material should also have an elongation sufficient to render the ribbon robust in various handling operations, such as in heat strip operations. Since the matrix material will most typically be in direct contact with the outermost coating on the fibers, it is also desirable that the matrix material release from the fibers when necessary, such as when repairing or branching is needed. The ability to access individual fibers in a ribbon matrix without damaging the fiber or any coating or identification thereon is an important feature. The ability to release, however, must be countered against the ability to adhere to the fibers during use. The matrix material should also have high resistance to thermal, oxidative and hydrolytic degradation. The ability to cure rapidly, such as upon exposure to UV radiation, can also be an important feature. Thus, there are a number of desirable characteristics for a matrix material, and it is often the case with compositions known in the art that improvement of one characteristic results in the sacrifice of another.
Similarly, secondary coatings used with optical fibers have a number of desirable characteristics. For example, such coatings should function as a hard, tough protective outer layer, preventing damage to the glass fiber during processing and use. A secondary coating should undergo minimal changes in physical properties upon exposure to organic solvents and moisture. A secondary coating should also have a coefficient of friction that facilitates winding and unwinding of the fibers on spools and allows the fibers to slide easily along each other in a cable structure, thus relieving stress, yet also allows the fibers to stay aligned on the spool.